Safety frame for sealing a heat-sealable film in a packaging machine

Abstract: A sealing frame (25) for a heat-sealable film, comprising a fixed portion (23) and a movable portion (24), the movable portion being articulated so that it can be moved close to the fixed portion by a movement actuator (13). A yieldable connecting device (10) is interposed between the actuator (13) and movable portion, which device (10) comprises one element (16) connected to the actuator and a second element (14) connected to the movable portion (24). The first and second elements are mutually hinged and a spring (18) is interposed therebetween. An electric switch (19) for stopping the actuator (13) movement in the direction of moving the frame portions close to each other is interposed between said first and second elements. The switch is thus operated when the spring compression exceeds a predetermined amount indicating the presence of obstacles to the movement of the movable portion (24).

Description: The present invention relates to a sealing frame the movements of which are executed in a safe manner. Packaging machines are known in which provision is made for a sealing frame designed to join together the peripheral edges of two sheets made of a heat sealable-material between which the goods to be packaged are interposed. The sealing frame generally comprises a fixed and a movable portion facing each other, wherein the movable portion is moved by actuators so that the plastics film is clamped between said two portions and sealing of same is carried out. Machines are known, for example, in which the movable portion of the sealing frame is comprised of a dome-shaped covering for a cell carrying out heat-shrinkage of the plastics film, so that cutting, sealing and heat-shrinkage of the package can be executed simultaneously. It will be recognized that when the frame (provided with a dome-shaped covering or not) is moved upwardly and downwardly automatically by a servo-mechanism, the unwary introduction of one hand into the operating field of the machine may be very dangerous. DE-2.520.475 discloses a sealing frame in which a protection element surrounds the movable portion. The protection element is resiliently supported on the movable portion. Upon mutual movement between the movable portion and the protection (for example, when the hand is introduced in the operating field) a switch is actuated and the movement of the movable portion is stopped. The general object of the present invention is to obviate the above mentioned drawback by providing a sealing frame provided with a mechanical safety linkage for carrying out movements of same, capable of avoiding the blades closing when an obstacle whatever is encountered, for example the operator's hands. In view of the above object, in accordance with the invention, a sealing frame for a heat-sealable film has been devised which comprises a fixed and a movable sealing portion, the movable portion being articulated so that it can be moved close to the fixed portion by a movement actuator for sealing a film between the sealing portions, characterized in that a yieldable connecting device is interposed between the movement actuator and movable portion, which device comprises one element connected to the actuator and a second element connected to the movable portion, said first and second elements being hinged on each other so that they mutually move on operation of the actuator at least in a direction in which the movable portion moves close to the fixed portion, the mutual movement taking place against the action of a spring disposed between the first and second elements for transmitting an operating force between the actuator and movable portion, an electric switch for stopping the actuator movement in said moving-close direction being interposed between said first and second elements, said switch being operated when the mutual movement exceeds a predetermined amount which is established as an indication that a transmission force of the spring exceeds a predetermined value, which means stopping of movement in a moving-close direction in the presence of obstacles to said movement. For better explaining the innovatory principles of the present invention and the advantages it offers over the known art, the description of a possible exemplificative embodiment applying such principles will be given hereinafter with the aid of the accompaying drawing in which the only figure is a fragmentary diagrammatic view of a sealing frame generally identified by reference numeral 25. The sealing frame 25 comprises a fixed portion 23 and a movable portion 24 carrying sealing blades for peripherally sealing a package formed of a pair of superposed plastics sheets containing a product to be packaged. The movable portion is articulated, so that it is movable by an actuator 13 between a raised position for introduction of the wrapped product into the frame and a lowered position juxtaposed to the fixed portion for peripheral sealing of the package. For example, the movable portion (which may also comprise a dome 11 for closing a cell carrying out hot air heat-shrinkage of the sealed package) is pivoted on an axis 12. Up to here a substantially known machine has been described; said machine is easily imaginable by any technician and therefore is not further described. The actuator 13 may comprise a reduction gear provided with a crank and connecting rod, a pneumatic device, etc. In an innovatory manner, a yieldable connecting device 10 is interposed between the movable arm 15 of the actuator and movable portion of the frame. In particular, the innovatory connecting device comprises a bracket or plate 14, integral with the portion to be moved, to which an oscillating lever 16 pivoted at one end on an axis 17, is connected. Pivotally mounted to the opposite end of the lever 16 is the actuator arm 15. A spring 18 is disposed between the bracket 14 and lever 16, which spring reacts in the opposite direction with respect to the direction of the frame closing movement. In particular, the spring will react so as to urge the lever 16 upwardly. The bracket 14 also supports a switch 19 the driving key 21 of which is operated when the lever 16 carries out a predetermined relative movement with respect to the bracket. The amount of the relative movement causing operation of the switch can be regulated by means of a screw 20 passing through the lever and acting on the switch. During its upward movement the lever abuts against an upper end-of-stroke console 22 projecting from the bracket, and the actuator movement is integrally transmitted to the dome. During the downward movement of the actuator arm, the lever 16 compresses the spring that transmits to the dome the force necessary to its descent movement. The spring 18 is such selected that its force or stiffness is capable of transmitting a sufficient reaction to the dome movement under normal conditions without the lever descent reaching and operating the switch driving key 21. If the lowering movement is hindered, the spring is further compressed, the screw 20 tail reaches the switch driving key 21 and the switch is therefore operated. As a technician can easily understand, the switch may be connected to a device 26 powering and controlling the actuator movement so that said actuator is immediately stopped and optionally the movement of same is reversed. In order to enable the frame to produce the necessary sealing pressure, without the safety contrivance being activated, a second switch 27 is provided for detecting reaching of the approached or closed position between movable and fixed portions. When the frame reaches its closed position, the switch 27 disables the switch 19, so that on stopping of the fixed portion against the movable portion, the switch 19 cannot inopportunely cause opening of the frame. In order to avoid the sealing pressure being completely discharged through the spring thereby damaging said spring, a limit stopper is provided for stopping movement of the lever 16 after said lever has carried out its movement for operating the switch 19. For example the limit stopper is embodied by a pin 28 coaxial with the spring and resting on the bracket 14 when the spring compression exceeds the amount necessary for operation of the switch 19. At this point it is clear that the intended purposes have been achieved by providing a safety frame the closure of which is prevented when an obstacle restrains movement of the movable portion. Of course, if the frame to be moved has a good balancing, the descent takes place freely or almost freely and the spring can be set so that its compression takes place at a relatively low pressure, the device intervention therefore occurring even when the smallest obstacle is present. Usually hot blades are present only on the fixed portion, the movable portion merely acting as a locating abutment. Therefore if the operator knock with his hands against the movable portion, this is not dangeours if the movement is stopped before the movable portion drags along the hands against the fixed portion. Obviously the above description applying the innovatory principles of the invention is given for purposes of illustration only and therefore must not be considered as a limitation of the scope of the invention as defined in the claims. For example, the switch may be of a type operated on moving the lever away therefrom instead of on moving said lever close thereto, and in this case it will be located uppermost relative to said lever.

Claims: A sealing frame (25) for a heat-sealable film comprising a fixed sealing portion (23) and a movable sealing portion (24), the movable portion being articulated so that it can be moved close to the fixed portion by a movement actuator (13) for sealing a film between the sealing portions (23, 24), characterized in that a yieldable connecting device (10) is interposed between the movement actuator (13) and movable portion, which device (10) comprises one element (16) connected to the actuator and a second element (14) connected to the movable portion (24), said first and second elements being hinged on each other so that they mutually move on operation of the actuator at least in a direction in which the movable portion moves close to the fixed portion, the mutual movement taking place against the action of a spring (18) disposed between the first and second elements for transmitting an operating force between the actuator and movable portion (24), an electric switch (19) for stopping the actuator (13) movement in said moving-close direction being interposed between said first and second elements, said switch being operated when the mutual movement exceeds a predetermined amount which is established as an indication that a transmission force of the spring exceeds a predetermined value, which means stopping of movement in a moving-close direction in the presence of obstacles to said movement. A frame according to claim 1, characterized in that the second element (14) is integral with the movable portion (24) and the first element is a lever (16) pivoted at one end thereof on the second element and pivotally connected at the other end to the actuator, which end reacts on the spring (18). A frame according to claim 2, characterized in that the second element is in the form of a supporting plate (14) to which the switch (19) body is fastened, a switch driving key (21) being disposed along the path of an actuating element (20) supported by the lever (16) for pressing the switch driving key (21) on movement of the lever a predetermined amount about its pivot point. A frame according to claim 3, characterized in that the actuating element (20) is embodied by the tail of a screw threadedly passing through the lever (16) in the direction of the lever movement towards the switch driving key (21), so that it carries out the adjustment of the predetermined amount of movement necessary for the switch operation. A frame according to claim 2, characterized in that the second element (14) comprises a first limit stopper (22) for stopping movement of the first element (16) in the direction opposite to that in which the fixed and movable portions move close to each other. A frame according to claim 1, characterized in that the movable portion (24) is pivoted according to a rotational axis, the actuator being a rectilinear actuator the connection of which enables the movable portion to rotate between a first and a second angular position. A frame according to claim 1, characterized in that the movable portion (24) defines a peripheral edge of a dome-shaped covering (11) for a cell carrying out heat-shrinkage in a packaging machine. A frame according to claim 1, characterized in that it comprises another switch (27) for detecting the frame closure, said second switch inhibiting the stopping effect produced by the first switch (19) on detection that a position close to the frame closure position has been reached. A frame according to claim 1, characterized in that it comprises a second limit stopper (28) stopping the mutual movement between the first and second elements, when the predetermined amount has been exceeded. A frame according to claim 9, characterized in that the second limit stopper (28) is a pin coaxial with the spring (18).

Inventors: TORRE FRANCESCO, TORRE, FRANCESCO
Applicants: MINIPACK TORRE SPA, MINIPACK-TORRE S.P.A.
Application year: 1994
Main classification: B65B57
IPC codes: B65B57, B29C65